#include <stdio.h>
#include <stdlib.h>
#include "crc.h"


const unsigned short genpoly16 = 0x8408;

// crc table
const unsigned short crc16_256_table[256] =
{
	0x0000, 
	0x1189, 
	0x2312, 
	0x329B, 
	0x4624,
	 0x57AD, 
	0x6536,
	 0x74BF,
	0x8C48, 
	0x9DC1, 
	0xAF5A,
	 0xBED3, 
	0xCA6C, 
	0xDBE5,
	 0xE97E,
	 0xF8F7,
	0x1081,
	 0x0108, 
	0x3393, 
	0x221A, 
	0x56A5, 
	0x472C, 
	0x75B7, 
	0x643E,
	0x9CC9, 
	0x8D40, 
	0xBFDB, 
	0xAE52, 
	0xDAED, 
	0xCB64, 
	0xF9FF, 
	0xE876,
	0x2102, 
	0x308B, 
	0x0210,
	 0x1399, 
	0x6726, 
	0x76AF, 
	0x4434,
	 0x55BD,
	0xAD4A, 
	0xBCC3, 
	0x8E58, 
	0x9FD1, 
	0xEB6E, 
	0xFAE7, 
	0xC87C, 
	0xD9F5,
	0x3183, 
	0x200A, 
	0x1291, 
	0x0318, 
	0x77A7, 
	0x662E, 
	0x54B5, 
	0x453C,
	0xBDCB, 
	0xAC42, 
	0x9ED9, 
	0x8F50,
	 0xFBEF, 
	0xEA66,
	 0xD8FD,
	 0xC974,
	0x4204, 
	0x538D,
	 0x6116, 
	0x709F,
	 0x0420, 
	0x15A9, 
	0x2732, 
	0x36BB,
	0xCE4C, 
	0xDFC5, 
	0xED5E, 
	0xFCD7, 
	0x8868, 
	0x99E1, 
	0xAB7A,
	 0xBAF3,
	0x5285, 
	0x430C, 
	0x7197, 
	0x601E, 
	0x14A1, 
	0x0528,
	 0x37B3,
	 0x263A,
	0xDECD, 
	0xCF44, 
	0xFDDF, 
	0xEC56, 
	0x98E9, 
	0x8960, 
	0xBBFB,
	 0xAA72,
	0x6306, 
	0x728F, 
	0x4014, 
	0x519D,
	 0x2522, 
	0x34AB, 
	0x0630, 
	0x17B9,
	0xEF4E, 
	0xFEC7,
	 0xCC5C, 
	0xDDD5, 
	0xA96A, 
	0xB8E3,
	 0x8A78,
	 0x9BF1,
	0x7387, 
	0x620E, 
	0x5095, 
	0x411C, 
	0x35A3,
	 0x242A, 
	0x16B1,
	 0x0738,
	0xFFCF, 
	0xEE46, 
	0xDCDD, 
	0xCD54, 
	0xB9EB, 
	0xA862,
	 0x9AF9, 
	0x8B70,
	0x8408, 
	0x9581,
	 0xA71A, 
	0xB693, 
	0xC22C,
	 0xD3A5, 
	0xE13E, 
	0xF0B7,
	0x0840, 
	0x19C9, 
	0x2B52,
	 0x3ADB, 
	0x4E64, 
	0x5FED,
	 0x6D76, 
	0x7CFF,
	0x9489, 
	0x8500, 
	0xB79B, 
	0xA612,
	 0xD2AD,
	 0xC324, 
	0xF1BF, 
	0xE036,
	0x18C1,
	 0x0948, 
	0x3BD3, 
	0x2A5A, 
	0x5EE5,
	 0x4F6C,
	 0x7DF7, 
	0x6C7E,
	0xA50A, 
	0xB483, 
	0x8618,
	 0x9791, 
	0xE32E,
	 0xF2A7, 
	0xC03C, 
	0xD1B5,
	0x2942,
	 0x38CB,
	 0x0A50, 
	0x1BD9, 
	0x6F66,
	 0x7EEF,
	 0x4C74, 
	0x5DFD,
	0xB58B, 
	0xA402, 
	0x9699,
	 0x8710,
	 0xF3AF, 
	0xE226, 
	0xD0BD, 
	0xC134,
	0x39C3, 
	0x284A, 
	0x1AD1, 
	0x0B58, 
	0x7FE7, 
	0x6E6E, 
	0x5CF5, 
	0x4D7C,
	0xC60C, 
	0xD785, 
	0xE51E,
	 0xF497,
	 0x8028, 
	0x91A1, 
	0xA33A, 
	0xB2B3,
	0x4A44,
	 0x5BCD,
	 0x6956, 
	0x78DF,
	 0x0C60, 
	0x1DE9, 
	0x2F72,
	 0x3EFB,
	0xD68D, 
	0xC704, 
	0xF59F, 
	0xE416,
	 0x90A9,
	 0x8120, 
	0xB3BB, 
	0xA232,
	0x5AC5, 
	0x4B4C, 
	0x79D7, 
	0x685E,
	 0x1CE1, 
	0x0D68, 
	0x3FF3,
	 0x2E7A,
	0xE70E, 
	0xF687, 
	0xC41C,
	 0xD595, 
	0xA12A, 
	0xB0A3, 
	0x8238, 
	0x93B1,
	0x6B46, 
	0x7ACF, 
	0x4854,
	 0x59DD,
	 0x2D62, 
	0x3CEB, 
	0x0E70, 
	0x1FF9,
	0xF78F, 
	0xE606,
	 0xD49D,
	 0xC514, 
	0xB1AB, 
	0xA022, 
	0x92B9, 
	0x8330,
	0x7BC7, 
	0x6A4E,
	 0x58D5,
	 0x495C,
	 0x3DE3, 
	0x2C6A, 
	0x1EF1, 
	0x0F78
};

// LSB-first transmission, the genpoly need be inversed.
// CRC-16 CCITT
// X^16 + X^12 + X^5 + 1

unsigned short cal_crc(unsigned char *data, int data_len, unsigned short init_val_of_crc)
{
	unsigned short crc = init_val_of_crc;

	while (data_len-- > 0)
	{
		crc ^= *data++;
		crc = (crc >> 8) ^ crc16_256_table[crc & 255];

	}

	return crc;
}
